RFC 3262 allows session descriptions to be exchanged in reliable provisional responses and in PRACK, so the session can be established before the call completes.

Checked 2026-09-24

Vendor
IETF
Product
SIP
Subsystem
offer/answer
Deployment
any
Region
not restricted
Release range
RFC 3262
Checked
2026-09-24

Sources

Cite this note

APA

WarmTransfer. (2026, September 24). Early media and ringback behavior: source note early-media-ringback-sdp-in-reliable-1xx. WarmTransfer. https://warmtransfer.net/knowledge/claims/early-media-ringback-sdp-in-reliable-1xx

BibTeX

@misc{warmtransfer-claim-early-media-ringback-sdp-in-reliable-1xx,
  title  = {Early media and ringback behavior: source note early-media-ringback-sdp-in-reliable-1xx},
  author = {{WarmTransfer}},
  year   = {2026},
  url    = {https://warmtransfer.net/knowledge/claims/early-media-ringback-sdp-in-reliable-1xx},
  note   = {Source note early-media-ringback-sdp-in-reliable-1xx, checked 2026-09-24}
}

Read in context